Background: Multiple case reports have pointed toward uncharacterized oral lesions, such as pulpitis, higher plaque index, necrotizing/desquamative gingivitis and others, in COVID-19 patients, suggesting that SARS-CoV-2 may worsen the manifestations of at least some oral viral infections. Our hypotheses were that COVID-19 would make oral manifestations of viral infections more common and that vaccination against Sars-CoV-2 might protect from developing such manifestations. Methods: We carried out a single-center, retrospective study, including patients from a dental and oral surgery center, studying adult and elderly patients with or without COVID-19 infection and vaccination. Results: As expected, Sars-CoV-2 infection was significantly less common among patients who received full vaccination against COVID-19: odds ratio 0.23, p< 0.001. In addition, herpetic gingivostomatitis was also less common among patients who received vaccination against COVID-19: odds ratio 0.18, p = 0.023. Developing COVID-19 itself did not have any significant correlation with developing herpetic gingivostomatitis: odds ratio 0.86, p = 0.9. Conclusions: We found that vaccination against Sars-CoV-2 markedly decreased the incidence of COVID-19 in our cohort of patients visiting a dentist’s office. In addition, such vaccination also decreased the rate of herpetic gingivostomatitis, while COVID-19 itself had no effect on it. COVID-19 itself, and vaccination against COVID-19, had no effect on the occurrence of oral manifestations of infectious mononucleosis or herpangina.